The objective of this study is to evaluate the effect of chemotherapy and oral antibiotics on gastrointestinal function in a population of patients with acute nonlymphocytic leukemia in remission. Eligible patients are those who are receiving the chemotherapy combination of thioguanine and cytosine arabinoside as maintenance chemotherapy and any of the following combinations of oral antibiotics for infection prevention: gentamicin plus nystatin; gentamicin plus vancomycin plus nystatin; nalidixic acid plus nystatin; trimethoprim sulfamethoxazole plus nystatin. The following laboratory tests are performed as a baseline, repeated at the end of the chemotherapy course and again when patients are given oral antibiotics: serum carotene, serum vitamin A, serum folic acid, serum D-xylose (2 hrs) and urine D-xylose (5 hrs). Sixteen patients have been entered on study. Seven patients have completed the sequence of laboratory tests. Eight patients failed to complete the tests, mostly due to the need for hospitalization to receive systemic empiric antibiotics. One patient remains on study. Additional patients will be entered on the study as they begin their maintenance courses of chemotherapy. It is too early to evaluate the data.